1. Field of the Invention
The present invention relates to a disk driving method and a disk drive, which stores and reads out information to/from a disk. In particular, it relates to one that can read out information in a short time.
2. Description of the Related Art
In recent years, CD-ROM drives have been drastically improved as multi-media systems have been popularized. In this situation, the demand for a high-speed disk drive, which drives a disk with a high revolving speed as fast as that of the ordinary disks, has been made. At the same time, the demand for a low-price disk drive has also been made.
In general, the digital disks such as the CD (Compact Drive) utilize the CLV (Constant Linear Velocity) control system so as to control the revolving speed of the disk. The CLV control system controls the revolving speed, thus maintaining the speed of reading out data stored in the disk, at any place including the inner circumference and the outer circumference. This requires that the revolving speed of the disk should be changed in accordance with the location of an optical pick-up, which reads in data, when the CLV control system is utilized.
When the optical pick-up is placed over the inner circumference, the revolving speed of the disk is equal to 550 rpm, whereas when it is placed over the outer circumference, the revolving speed of the disk is equal to 200 rpm. Accordingly, when the optical pick-up is moved from the outer circumference o the inner circumference, a correction is needed for the difference of 350 rpm. In order to make the access time to the disk shorter, there are two measures that can be taken. That is to say, the first one is to increase the torque of the spindle motor. The second one is to expand the capture range of a PLL (Phase Lock Loop) circuit, which is used to help in reading out a detected signal, so as to shorten the lock-on time.
However, the method of expanding the capture range, so as to shorten the lock-on time, has been coming to a deadlock. Accordingly, a solution that is different from the conventional has become necessary. Generally, strengthening the loop gain or speeding up the response can attain the improvement in the lock-on time. However, this causes the PLL circuit to react excessively to a possible noise and/or signal error, according to either one of the two solvable ways above. As a result, neither of the two ways is preferable for solving the above problem.
According to the conventional CD-ROM drive, as described above, the rotating speed of the disk needs to be changed into the speed corresponding to the location of the optical pick-up in a radius direction of the disk. However, it takes a long time for the spindle motor, which rotates the disk, to change its own rotating speed to another, thus causing a longer accessing time.
Using the conventional PLL circuit, the phase comparator outputs a DISABLE signal while the optical pick-up is moved (seeks), and outputs an ENABLE signal immediately after the optical pick-up has been moved. These operations are performed so as to prevent the PLL circuit from being locked on a different frequency during a seeking operation. During the seeking operation, since valid data discontinuously appears, the PLL circuit may be incorrectly locked on if the comparator does not output the DISABLE signal. After the optical pick-up is done seeking, the operation of the PLL circuit enters the tracking mode. In this mode, the rotating speed of the spindle motor is controlled in such a manner that the frequency of the data bits read out from the disk can fall within the capture range of the PLL circuit. After the PLL circuit has entered the locked-on mode, the data (or bits of data) can be reproduced.
However, since the conventional PLL circuits have a narrow capture range from plus to minus several percents, it takes a long time for them to become able to reproduce data. As a result, the seeking time becomes longer. In other words, the time ranging from the point of time the frequency of the data bits enters the capture range after the optical pick-up is moved (seeks), to the point of time when the PLL circuit enters the locked-on mode, is long. On the other hand, even if it has a wide capture range, the PLL circuit is locked on the frequency of an EFM (Eight to Fourteen Modulation) signal, which is the one before the optical pick-up is moved. Therefore, it also takes the CD-ROM drive a long time to become able to reproduce data. As a result, the seeking time becomes longer. Moreover, the time until the PLL circuit enters the lock-on mode, becomes longer after the optical pick-up is moved (seeks) again.
In order to shorten the above time (the data access time), the torque of the spindle motor is increased so that the rotating speed of the disk can reach the target speed. Alternatively, the capture range of the PLL circuit is enlarged or the lock-on time of the PLL circuit is shortened. However, the diameter and height of the motor restrict the increase in torque. In addition, this increase causes an increase in power consumption. Moreover, there are many problems left for enlarging the capture range and lock-on time of the PLL circuit. Thus, there is a limit in solving the above problems according to the above conventional approaches.
The present invention has been made by taking the above problems into account. Accordingly, an objective of the present invention is to provide a disk driving method and a disk drive, which can access a disk in a short time without enlarging the capture range and shortening the lock-on time. Another objective of the present invention is to provide a disk driving method and a disk drive, which can access a disk in a short time after the seeking operation, without increasing the power dissipation.
To attain the above objectives, according to an aspect of the present invention, a disk drive is provided, comprising: a signal detector with a pick-up (2, 9), which detects a signal from a disk; and a PLL unit (11), which functions so as to lock a clock signal on the signal, which has been detected by the signal detector, within the time the pick-up stays within a track region of a disk (1), but not within the time when the pick-up stays within a mirror region of the disk, during the seeking operation of the pick-up. The above reference numerals in parentheses are attached to their respective corresponding elements in FIG. 1.
According to another aspect of the present invention, a disk driving method is provided, comprising the steps of: detecting a signal from a disk (1); and functioning so as to lock a clock signal on the signal detected, within the time when a pick-up stays within a track region of a disk (1), but not within the time when the pick-up stays within a mirror region of the disk (1) during the seeking operation of the pick-up. The above reference numerals in parentheses are attached to their respective corresponding elements in FIG. 1.